1. Field of the Invention
The present invention is generally related to a method for protecting a marine propulsion system and, more particularly, to a method which inhibits galvanic corrosion from damaging a marine propulsion system and, in addition, inhibits the growth of marine organisms on certain surfaces of the marine propulsion system.
2. Description of the Prior Art
Those skilled in the art of marine propulsion systems are aware of several problems that can adversely affect the enjoyment of owning and operating a marine vessel. One problem concerns the deleterious effects caused by galvanic circuits that can occur when different metals are submerged proximate each other in a water environment. This problem is exacerbated when the marine propulsion system is used in saltwater. Another problem relating to the operation of marine vessels is the growth of marine organisms on submerged surfaces of both the marine propulsion system and the vessel itself. In seawater, these organisms include many different types of organisms, including barnacles. In non-saltwater applications, the organisms can comprise algae and zebra mussels.
Many different techniques and procedures have been developed to address both the problem of galvanic corrosion and marine fouling.
U.S. Pat. No. 3,953,742, which issued to Anderson et al. on Apr. 27, 1976, discloses a cathodic protection monitoring apparatus for a marine propulsion device. The system monitor is coupled to an impressed current cathodic protection circuit used for corrosion protection of a submerged marine drive. The cathodic protection circuit includes one or more anodes and a reference electrode mounted below the water line and connected to an automatic controller for supplying an anode current which is regulated in order to maintain a predetermined reference potential on the protected structure. A switch selectively connects a light emitting diode lamp or other light source between the controller output and ground so that the controller current may, when tested, be used to operate the light source in order to confirm that power is available to the anode.
U.S. Pat. No. 4,322,633, which issued to Staerzl on Mar. 30, 1982, discloses a marine cathodic protection system. The system maintains a submerged portion of a marine drive unit at a selected potential to reduce or eliminate corrosion thereto. An anode is energized to maintain the drive unit at a preselected constant potential in response to the sensed potential at a closely located reference electrode during normal operations. Excessive current to the anode is sensed to provide a maximum current limitation. An integrated circuit employs a highly regulated voltage source to establish precise control of the anode energization.
U.S. Pat. No. 4,492,877, which issued to Staerzl on Jan. 8, 1985, discloses an electrode apparatus for cathodic protection. The apparatus is provided for mounting an anode and reference electrode of a cathodic protection system on an outboard drive unit. The apparatus includes an insulating housing on which the anode and reference electrode are mounted and a copper shield mounted between the anode and electrode to allow them to be mounted in close proximity to each other. The shield is electrically connected to the device to be protected and served to match the electrical field potential at the reference electrode to that of a point on the outboard drive unit remote from the housing.
U.S. Pat. No. 4,528,460, which issued to Staerzl on Jul. 9, 1985, disclosed a cathodic protection controller. The control system for cathodically protecting an outboard drive unit from corrosion includes an anode and a reference electrode mounted on the drive unit. Current supplied to the anode is controlled by a transistor, which in turn is controlled by an amplifier. The amplifier is biased to maintain a relatively constant potential on the drive unit when operated in either fresh or salt water.
U.S. Pat. No. 4,872,860, which issued to Meisenburg on Oct. 10, 1989, discloses a sacrificial anode for marine propulsion units. It is disposed in association with the trim cylinder unit of a marine propulsion device and is positioned in the previously unused area between the aft cylinder end and the rodeye or the like on the piston rod end. More specifically, the anode is in the form of an elongated generally cylindrical member of a diameter approximately that of the trim cylinder to provide improved mass characteristics, and is deeply grooved to thus provide ribs which enhance the working surface area.
U.S. Pat. No. 5,342,228, which issued to Magee et al. on Aug. 30, 1994, discloses a marine drive anode. The drive is provided with a large volume anode for galvanic protection. The anode is a brick-like block member tapered along each of its height, width, and length dimensions.
U.S. Pat. No. 6,173,669, which issued to Staerzl on Jan. 16, 2001, discloses an apparatus and method for inhibiting fouling of an underwater surface. The fouling prevention system comprises two conductive surfaces and a device that alternates the direction of electric current between the two surfaces. The current is caused to flow through seawater in which the two surfaces are submerged or partially submerged. A monitor measures the current flowing from one of the two conductive surfaces and compares it to the current flowing into the other conductive surface to assure that no leakage of current of substantial quantity exists.
U.S. Pat. No. 6,183,625, which issued to Staerzl on Feb. 6, 2001, discloses a marine galvanic protection monitor. The system uses two annunciators, such like light emitting diodes, to alert a boat operator of the current status of the boat's galvanic protection system. A reference electrode is used to monitor the voltage potential at a location in the water and near the component to be protected. The voltage potential of the electrode is compared to upper and lower limits to determine if the actual sensed voltage potential is above the lower limit and below the upper limit. The two annunciator lights are used to inform the operator if the protection is proper or if the component to be protected is either being overprotected or underprotected.
U.S. Pat. No. 6,209,472, which issued to Staerzl on Apr. 3, 2001, discloses an apparatus and method for inhibiting fouling of an underwater surface. The system for inhibiting marine organism growth on underwater surfaces provides an electric current generator which causes an electric current to flow proximate the underwater surface. A source of power, such as a battery, provides electrical power to the electric current generator. The flow of current passes from the underwater surface through the water surrounding the surface or in contact with the surface, and a point, of ground potential. The point of ground potential can be a marine propulsion system attached to a boat on which the underwater surface is contained.
U.S. Pat. No. 6,547,952, which issued to Staerzl on Apr. 15, 2003, discloses a system for inhibiting fouling of an underwater surface. An electrically conductive surface is combined with a protective surface of glass in order to provide an anode from which electrons can be transferred to seawater for the purpose of generating gaseous chlorine on the surface to be protected. Ambient temperature cure glass (ATC glass) provides a covalent bond on an electrically conductive surface, such as nickel-bearing paint.
U.S. patent application Ser. No. 10/632,056, (M09691), which was filed on Jul. 31, 2003 by Staerzl et al., discloses a submersible anode made of a resin matrix with a conductive powder supported therein. An anode for a cathodic protection system comprises a base portion or support structure which is shaped to receive a conductive element, or insert, within a cavity of the support structure. The conductive element is made of a polymer material, such as vinyl esther, with a conductive filler, such as graphite powder. The base is attachable to a marine vessel or other submersible component that is being protected by a cathodic protection system. The anode allows the use of a relatively inexpensive resin material with a graphite filler in place of a much more expensive platinum coated titanium element.
U.S. patent application Ser. No. 10/780,342, (M09719), which was filed on Feb. 17, 2004 by Misorski et al., discloses a marine drive unit which is overmolded with a polymer material. A marine propulsion system drive unit is provided with a polymer layer to protect its outer surface from abrasion and corrosion. The polymer layer is injection molded around the outer surface of a metallic gear case structure or drive shaft housing to provide a coat which is approximately three millimeters thick and which will resist scratching and corrosion. The polymer layer can be a glass filled polymer or a carbon filled polymer. An adhesion promoter can be used to enhance the bonding and intimate contact between the inner surface of the polymer layer and the outer surface of the metallic gear case structure or drive shaft housing.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
It would be significantly beneficial if a system could be provided which enhances the operation of a cathodic protection system by enlarging the size of the anode. It would be particularly beneficial if this size expansion could be achieved without the necessity of attaching relatively large components to the transom of a marine vessel in place of the normal anode used in most commercially available cathodic protection systems. It would also be beneficial if a system could be provided to protect the drive unit of a marine propulsion system from marine fouling in both saltwater and non-saltwater environments.